Oscillators are commonly implemented within wireless communication devices that transmit and receive wireless signals. For example, an oscillator is commonly used within a frequency synthesizer in a wireless communication device to generate carrier waveforms. Baseband signals are modulated on the carrier waveforms, and then the modulated carrier waveforms are transmitted to other devices as wireless signals. The receiving device uses an oscillator to synthesize the carrier and remove the baseband signal for demodulation. Oscillators are of paramount importance to wireless communication. Oscillators are also used in many other applications, including wired communication applications.
Conventional oscillators typically use a varactor that is controlled via a phase-locked loop (PLL). Unfortunately, such voltage controlled oscillator (VCO) designs require the use of analog circuitry or components, which are often undesirable. Furthermore, it is very difficult to improve the performance of VCOs, e.g., due to difficulties in reducing supply voltages and complexities associated with the charge-pump and analog filter. For these reasons, digitally controlled oscillators (DCOs) have been developed for some applications.